The long term goal of this project is to understand the coordinated activity of pancreatic islet cells and the role of gap junctions in communication between them. An initial step will be the biophysical characterization of gap junctions between homologous and heterologous islet cells. Direct study of gap junctions in the intact islet has - been difficult, since the cells are very small ( 10-12 um diameter ) and their gap junctions are distributed nonuniformly in a complex - three dimensional array. Therefore it is important to develop and experimental approach that allows direct measurement of junctional properties. For electrical and permeability measurements pairs of identified pancreatic cells would be the optimum preparation, and we intend to develop a system in which cell pairs can be studied routinely in - vitro. We will use immunofluorescent probes to identify cell type B, A, D or PP, and we will analyze properties such as pH, Ca2+, voltage and cAMP dependence which are known to be important in other tissues. In addition, there is a distinct set of pharmacological agents acting on islet cells including, for example, glucose and glybenclamide. There is evidence that these secretagogues increase the incidence of gap junctions and/or dye coupling but precise characterization of junctional properties has not yet been carried out. The in vitro system will be used to search for specific blockers of junctional permeability - between islet cells and for controls of junctional formation and removal. A knowledge of intercellular communication between islet cells is likely to be essential for understanding of islet function in normal as well as pathological conditions.